Numerous materials are packaged in flexible containers, such as flexible pouch-like containers. Such pouches may be formed from pairs of webs which are heat sealed to one another. Alternatively, the pouch may be formed from a single web which is folded, with the side seams and top seam, and optionally the folded bottom edge, being heat sealed. Such pouch-like containers may be fabricated from thermoplastic resins or laminates including inner heat-sealable layers fabricated from thermoplastic resins. Thus, pouches are commonly formed from a pair of lamina in which each lamina comprises an outer layer of a plastics resin film, a central barrier layer of a metallic foil, such as aluminum foil, and an inner layer of a heat-sealable thermoplastic resin film, or from folded webs of these sheet materials.
In filling and heat sealing pouches with foodstuffs and the like, contamination of the top edge region of the pouch, which is the area where the final seal is to be formed, is a continuing problem. Quite often, solid food particles will cling to the walls of the pouch in the edge region where this final heat seal is to be located. This contamination requires that the region to be heat sealed be cleaned of food particles prior to sealing, since these particles will interfere with the heat sealing operation, causing gaps, blisters, blemishes or other defects in the heat seal and possible failure in the seal, which seal must be a hermetic seal. Such cleaning has in the past been accomplished by means of pressurized steam. While pressurized steam successfully cleanses the edge region which is to be heat sealed from solid food particles, the steam which is employed presents a sealing problem of its own. Moisture now present in the heat seal region can cause blister defects in the seal, due to entrapment of the moisture in the sealing region and the conversion of this moisture in the sealing region to steam under pressure by the heated pressurizing sealing bars, and thus also cause failures in the heat seal, preventing a hermetic seal from being produced. Thus, it is a primary object of the present invention to improve the final hermetic heat seal formed on a filled pouch by elimination of these moisture-caused defects.